This project is concerned with developing basic information on the ultrastructural morphology and properties of tooth enamel, using transmission and scanning electron microscopy, as well as other related physical methods. A special feature of the study is the capability of preparing thin sections of etched or fully calcified enamel for transmission electron microscopy from the same areas that are observed by scanning microscopy. Objectives are to obtain a precise and detailed body of information on the basic prismatic and crystalline structures in enamel, their variations, and new information on the relation between structural organization and solubility properties. Regions of higher organic content near the dentino-enamel junction, as well as the development and maturation of the prism border area will be studied. A correlated microradiographic-electron microscopic study of caries will be carried out. The study will also extend to investigate the effects of chemotherapeutic agents such as tetracyclines and fluorides.